The present invention relates to a computer-system tablet input device which reads the address data of patterns or characters.
In a prior art tablet input device, connected to a drive circuit are a plurality of drive loops or a plurality of geometric parallel drive lines two of which may form a drive loop, and a plurality of sense loops or a plurality of parallel sense lines two of which may form a sense loop arrayed perpendicular to the drive loops or lines and connected to a sense circuit. The drive and sense circuits in turn are connected to a decode circuit which converts into the scanning pulses the address data (that is, the numbers of the drive and sense lines) of the drive and sense lines. In response to the scanning pulses from the decode circuit, the drive circuit sequentially selects the drive loops and passes a drive current through the selected drive loop. In like manner, in response to the scanning pulses from the decode circuit the sense circuit sequentially selects the sense loops.
When one touches with an input pen having a magnetic tip a rectangular region or address defined by one of the drive or sense loops, the electromagnetic coupling between the drive and sense loops associated with the selected region or address is increased so that when the associated drive loop is selected and excited, a voltage which exceeds a predetermined threshold level is induced across the associated sense loop. The sense circuit detects this induced voltage and transmits a detect signal to the decode circuit so that the decode circuit may output the numbers of the associated drive and sense loops in a coded form.
With the prior art input device with the number of m drive loops and the number of n sense lines, one scanning of the face of the manipulation pad requires the selection and excitation of the drive loops m times and the number of (m.times.n) times of selection and detection of the sense loops. In case of reading complex patterns and characters such as kanji, the input items are increased and a high resolution is required. Therefore the drive and sense loops must be increased in number so that the scanning time is inevitably increased, resulting in unsatisfactory operability or manipulability.